1. Field of the Invention
This invention relates in general to a radar device and in particular to a radar device utilizing a non-constantly scanning radar antenna having a circular arrangement for reducing interference caused by a ground reflection.
2. Description of the Prior Art
As described at pages 35-12 to 35-14 of the publication entitled "Radar Handbook" by Skolnik (McGraw-Hill, 1970) describes the manner of processing scanning sequences employing filters so as to suppress ground echoes in moving target indicators (MTI), and particularly in the case of non-constant spatial scanning by the antenna the so-called "step scan method". The scanning sequence must be of sufficient length to allow the build-up effect of the filter to die away. This effect reduces the discovery of objects having a slow radial movement in zones subject to ground reflection which is possible because of the omission of the scanning modulation of the interference echoes and also prevents the use of sequential detection processes such as described for example on pages 15-19 to 15-27 of the above referenced "Radar Handbook".
Pages 1551-1552 from the Proceedings of the IEEE, Vol. 60, No. 12 dated December 1972 discloses recursive filters for suppressing ground echoes which have a desirable pass characteristic and can be improved relative to their build-up behaviour by the input of a substitute value equal to the first scanning value. Even with this measure, in the event of a deviation in the following scanning values from the first scanning value, a build-up process occurs which causes the intensity to be proportional to the extend to which the filter is designed for the discovery of objects carrying out a slow radial movement. The recursion weights of the filter must be matched to a given number of scanning values and this impairs the practical use of such apparatus in sequential detection processes and apparatus.